PathTools: use PerlLIO_*() functions and chdir() on a symlink differences

PathTools: use PerlLIO_*() functions and chdir() on a symlink differences

Use PerlLIO_lstat() and PerlLIO_readlink() instead of directly calling
the POSIX names, so our Win32 overrides work.

For the test, unlike POSIX, changing directory via a symlink on Win32
appears to store the symlink as part of the current directory rather
so GetCurrentDirectory() fetches that rather than the hardlinked path.